There are different types of leucocytes in the peripheral blood of a healthy person, i.e., lymphocyte, monocyte, neutrophil, eosinophil, and basophil. Furthermore, lymphocyte is roughly classified into three types referred to as subsets (T-lymphocyte, B-lymphocyte, NK-lymphocyte).
B-lymphocyte is a bone marrow-derived lymphocyte and has immunoglobulin on its surface. B-lymphocyte plays a very important role in the immune function of a human body, for example, it differentiates into a plasma cell and produces an antibody. T-lymphocyte is a thymus-derived lymphocyte and does not have an immunoglobulin on its surface. T-lymphocyte plays an important role in regulating the immune system, and it is known that a T-lymphocyte defect often causes immunodeficient, autoimmune, allergic, and proliferative immune disorders.
As described above, B-lymphocytes and T-lymphocytes are greatly involved in the immune system. Therefore, checking an increase or decrease in B-lymphocyte and T-lymphocyte allows a change in immune function to be known. B-lymphocytes and T-lymphocytes are present in a specific ratio, but it can change due to the presence of a disease. Therefore, measuring the ratio of B-lymphocytes to T-lymphocytes allows useful information regarding the presence of a disease to be obtained.
Examples of diseases that show increased B-lymphocytes include multiple myeloma, B-lymphocytic chronic lymphocytic leukemia, infectious mononucleosis, Burkitt's lymphoma, and the like. Examples of diseases that decrease B-lymphocytes include AIDS, advanced cancer, Hodgkin's lymphoma, alymphocytic hypoimmunoglobulinemia, agammaglobulinemia, reticular dysgenesis, measles, varicella, herpes, and the like.
Examples of diseases that show increased T-lymphocytes include ATL, Sezary syndrome, infectious mononucleosis, agammaglobulinemia, and the like. Examples of diseases that decrease T-lymphocytes include AIDS, advanced cancer, alymphocytic hypoimmunoglobulinemia, and the like.
As a leucocyte classification method that uses flow cytometry, Patent Document 1 discloses a method for classifying leucocytes into five types and counting the number thereof in which a blood sample is treated with a hemolyzing agent that contains a cationic surfactant and a nonionic surfactant and a fluorescent dye that stains nucleic acid. However, Patent Document 1 completely fails to describe measurement of B-lymphocytes and T-lymphocytes.
Lymphocyte classification/counting attained by performing flow cytometry on lymphocytes that are labeled with a fluorescence-labeled antibody is already known as a technique for classifying/counting lymphocytes (Patent Document 2).